There has been a worrisome increase in fighting between rebel and government forces in Sudan's conflict-torn western Darfur region, the U.N. chief said in a report published on Monday.

"I am deeply concerned over the upsurge in fighting between government and (rebel) movement forces ... and its humanitarian consequences," Secretary-General Ban Ki-moon said in a quarterly report on the U.N.-African Union peacekeeping force in Darfur, known as UNAMID.

Ban said he was particularly worried about the fighting between government forces and the rebel Justice and Equality Movement (JEM) and the faction of the Sudan Liberation Army (SLA) loyal to Minni Minnawi. Last week Sudan's army said it clashed with fighters from JEM and Minnawi's SLA faction in a four-hour fight that left 21 people dead.

A string of cease-fires and accords has failed to stop the fighting in the remote western territory where mostly non-Arab rebels took up arms against the government in 2003. JEM rejoined fitful Darfur peace talks in December, seven months after walking out of the negotiations.

Although UNAMID is nearing deployment of its mandated full strength of 26,000 troops and police, Ban complained that Khartoum has been delaying the issue of visas for non-Arabic-speaking police officers and other personnel. (…)

He also urged Khartoum to lift restrictions for humanitarian workers trying to reach people in the remote Jebel Marra region. Ban said civilians in Jebel Marra "have been cut off from humanitarian assistance for almost one year."

Separately, UNAMID said on Sunday that the Sudanese government had failed to honor an agreement to notify the peacekeeping force about an extensive cordon-and-search operation in the Zam Zam displaced persons camp in Darfur.

"The operation resulted ... in the arrest of 37 individuals, for reasons unknown, the impounding of ten 4x4 vehicles, the seizure of three assault rifle magazines, unspecified quantities of ammunitions, and suspected stolen goods and illegal substances," UNAMID said in a statement.

Darfur activists and human rights groups have urged the United Nations and United States to step up efforts to secure peace in Darfur, where U.N. officials estimate that as many as 300,000 people have died since 2003. (…)

Activists and rights groups say that U.S. and U.N. officials have focused on north-south Sudan tensions due to the referendum on southern independence that took place earlier this month but now need to pay more attention to Darfur.

"The United States and international community must act to stop future violence and to ensure humanitarian access to care for these displaced people in Darfur while continuing high level engagement on north-south issues," said Amir Osman of the Genocide Intervention Network/Save Darfur Coalition.